The amount of wireless data utilized in mobile networks has increased dramatically in the last few years, pushing the capacity of current macro cellular deployments. Cellular communications systems, which utilize microwave spectrum bands (300 MHz to 3 GHz), are becoming capacity-limited due to interference and traffic load. The use of high frequency bands, where vast amounts of bandwidth is available, is considered to be a crucial technology for future generation communication systems. The use of these frequency bands (e.g., 28, 38, 60 and 73 GHz) can mitigate the problem of capacity currently observed.
Propagation in the millimeter band (mmWave) is much more challenging than in the microwave band, resulting in a more stringent link budget at a mmWave band than at a microwave band. Equipping both the transmitter and receiver with a larger number of antenna arrays is a viable solution to compensate for the mmWave extra path loss by beamforming.
Since antenna size is inversely proportional to the carrier frequency, the use of these high frequency bands reduces the antenna size considerably. This opens the door to employ a larger number of transmit and receive antenna arrays at both network and terminal sides.
Hybrid antenna architecture may be used to trade off hardware complexity, power consumption, and the performance and coverage of the system. Hybrid antenna architecture typically includes analog (phase shifter) and digital (baseband pre-coder) beamforming parts.
A base station may include one or more Radio Frequency (RF) chains, and each RF chain is connected to analog phase shifters and antenna arrays. A user equipment (UE) receiver may include one or more RF chains connected to receiver analog phase shifters and antenna arrays.
There are different types of analog beamforming architectures. Two such architectures are shared array and sub-array.